<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
      .login-header {
        width: 100%;
        text-align: center;
        height: 30px;
        font-size: 24px;
        line-height: 30px;
      }

      ul,li,ol,dl,dt,dd,div,
      p,span,h1,h2,h3,h4,
      h5,h6,a {
        padding: 0px;
        margin: 0px;
      }

      .login {
        display: none;
        width: 512px;
        height: 280px;
        position: fixed;
        border: #ebebeb solid 1px;
        left: 50%;
        top: 50%;
        background: #ffffff;
        box-shadow: 0px 0px 20px #ddd;
        z-index: 9999;
        transform: translate(-50%, -50%);
      }

      .login-title {
        width: 100%;
        margin: 10px 0px 0px 0px;
        text-align: center;
        line-height: 40px;
        height: 40px;
        font-size: 18px;
        position: relative;
        cursor: move;
      }

      .login-input-content {
        margin-top: 20px;
      }

      .login-button {
        width: 50%;
        margin: 30px auto 0px auto;
        line-height: 40px;
        font-size: 14px;
        border: #ebebeb 1px solid;
        text-align: center;
      }

      .login-bg {
        display: none;
        width: 100%;
        height: 100%;
        position: fixed;
        top: 0px;
        left: 0px;
        background: rgba(0, 0, 0, 0.3);
      }

      a {
        text-decoration: none;
        color: #000000;
      }

      .login-button a {
        display: block;
      }

      .login-input input.list-input {
        float: left;
        line-height: 35px;
        height: 35px;
        width: 350px;
        border: #ebebeb 1px solid;
        text-indent: 5px;
      }

      .login-input {
        overflow: hidden;
        margin: 0px 0px 20px 0px;
      }

      .login-input label {
        float: left;
        width: 90px;
        padding-right: 10px;
        text-align: right;
        line-height: 35px;
        height: 35px;
        font-size: 14px;
      }

      .login-title span {
        position: absolute;
        font-size: 12px;
        right: -20px;
        top: -30px;
        background: #ffffff;
        border: #ebebeb solid 1px;
        width: 40px;
        height: 40px;
        border-radius: 20px;
      }
    </style>
  </head>

  <body>
    <div class="login-header">
      <a id="link" href="javascript:;">点击，弹出登录框</a>
    </div>
    <div id="login" class="login">
      <div id="title" class="login-title">
        登录会员
        <span
          ><a id="closeBtn" href="javascript:void(0);" class="close-login"
            >关闭</a
          ></span
        >
      </div>
      <div class="login-input-content">
        <div class="login-input">
          <label>用户名：</label>
          <input
            type="text"
            placeholder="请输入用户名"
            name="info[username]"
            id="username"
            class="list-input"
          />
        </div>
        <div class="login-input">
          <label>登录密码：</label>
          <input
            type="password"
            placeholder="请输入登录密码"
            name="info[password]"
            id="password"
            class="list-input"
          />
        </div>
      </div>
      <div id="loginBtn" class="login-button">
        <a href="javascript:void(0);" id="login-button-submit">登录会员</a>
      </div>
    </div>
    <!-- 遮盖层 -->
    <div id="bg" class="login-bg"></div>


    
    <script>
      var loginBg = document.querySelector("#bg");
      var loginLink = document.querySelector("#link");
      var loginBox = document.querySelector("#login");
      var closeBtn = document.querySelector("#closeBtn");
      loginLink.addEventListener("click", function () {
        loginBox.style.display = "block";
        loginBg.style.display = "block";
      });
      closeBtn.addEventListener("click", function () {
        loginBox.style.display = "none";
        loginBg.style.display = "none";
      });

      // 拖动事件的三个过程：鼠标按下mousedown,鼠标移动mousemove,鼠标松开mouseup

      // 模态框跟着鼠标走的原理：
      var loginTitle = document.querySelector("#title");
      loginTitle.addEventListener("mousedown", function (e) {
        // 当鼠标按下时，需要立即得到鼠标在盒子中的坐标
        var x = e.pageX - loginBox.offsetLeft;
        var y = e.pageY - loginBox.offsetTop;
        // 为整个页面添加鼠标移动事件
        // 之所以不为loginBox添加mousemove事件，是因为鼠标若移动得太快，则会立即脱离登录盒子，
        // 此时再移入盒子，又会再次触发mousemove事件，出现不按鼠标仍能移动盒子得怪异现象。
        // 而将mousemove事件绑定在document上就不会出现这样的鼠标脱离‘事件所绑定的元素’的情况
        document.addEventListener("mousemove", move);

        function move(e) {
          // 模态框的left和top等于鼠标在页面的坐标减去鼠标在盒子内的坐标
          login.style.left = e.pageX - x + "px";
          login.style.top = e.pageY - y + "px";
        }
        // 鼠标松开时取消整个页面的鼠标移动事件
        document.addEventListener("mouseup", function (e) {
          document.removeEventListener("mousemove", move);
        });
      });
    </script>
  </body>
</html>
